Alleviation on battery thermal runaway propagation : effects of oxygen level and dilution gas

Abstract

The thermal safety issue of the lithium-ion batteries (LIBs) is a key challenge in new energy storage systems, and novel protection strategies for battery fire and explosions are urgently needed. In this experimental study, the thermal runaway and fire behaviors of cylindrical LIBs are explored in the ambient oxygen concentration from 12% to 21% with the dilution gas of nitrogen and argon. The X-ray CT imaging and energy-dispersive spectrometry are used to assist the micro morphology analysis. The results show that the thermal runaway time interval (between Layers 1 and 2) increases from 136 s (21% O2) to 196 s (12% O2), indicating the thermal-runaway propagation rate is reduced by 44%. Moreover, the mass loss and flaming combustion are both weakened when reducing the oxygen concentration. Whereas, the oxygen concentration has little influence on the maximum cell temperature during thermal runaway (600–800 °C). Comparison between nitrogen and argon dilutions shows a similar effectiveness in alleviating thermal runaway propagation, so the nitrogen dilution is more cost effective. The X-ray CT imaging and energy-dispersive spectrometry show less molten drops and much less fluorine in the burnt cell at a higher oxygen level. This study provides new references for improving the safer transport and storage of battery modules and fire protection strategies.